Enhancement of static magnetic field on nitrogen removal at different ammonium concentrations in a sequencing batch reactor: Performance and biological mechanism

This study aimed to investigate the effects and biological mechanism of external static magnetic fields (SMFs) on enhancing nitrogen removal at different influent ammonium nitrogen (NH₄⁺) concentrations. Four sequential batch reactors (SBRs) with SMFs of 0, 15, 30, and 50 mT were operated continuously for 196 days, during which the influent NH₄⁺-N concentration increased stepwise as 50, 100, 350, and 600 mg L^-1. The results showed that 50 mT had optimum effects on enhancing nitrogen removal, especially at high NH₄⁺-N concentrations (350 and 600 mg L^-1). The biological mechanism by which SMF influences nitrogen removal varies depending on the NH₄⁺ concentration. At low NH₄⁺-N concentrations (50 and 100 mg L^-1), a field of 50 mT increased key enzyme activities and corresponding functional gene abundances. Additionally, it further improved functional bacterial abundances, which involved nitrifying and denitrifying bacteria at high NH₄⁺ concentrations. These findings could provide guidance for the selection of optimum SMF intensity at different influent NH₄⁺ concentrations.

Trichloroethylene inhibits nitrogen transformation and microbial community structure in Mollisol

Trichloroethylene (TCE) is the most ubiquitous halogenated organic pollutant in the environment, it is one of the 129 priority control pollutants. In order to clarify the influence of TCE on microorganisms and nitrogen transformation in Mollisol is the core purpose of this study. Results showed that 10 mg kg^-1 TCE is the concentration limit of ammonification in Mollisol. When the concentration of TCE reached 10 mg kg^-1 and the effect lasted for over 7 days, the process of ammonia oxidation to nitric acid in Mollisol will be affected. TCE affected the process of nitrate (NO₃^-) transformation into nitrite (NO₂^-) by affecting the activity of nitrate reductase, thereby affected the denitrification process in soil. When the concentration of TCE is more than 10 mg kg^-1 it reduced the ability of soil microorganisms to obtain nitrogen, thereby affecting soil nitrogen transformation. RDA (Redundancy analysis) showed that the activity of nitrate reductase and the number of nitrifying bacteria and denitrifying bacteria in soil was negatively correlated with the incubation of TCE. In addition, soil nitrate reductase, nitrite reductase, peroxidase activity, ammonifying bacteria, nitrifying bacteria and denitrifying bacteria were negatively correlated with TCE concentration. Beyond that PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) of functional gene structure depend on KEGG (Kyoto Encyclopedia of Genes and Genomes) showed that 20 mg kg^-1 TCE significantly inhibited the metabolism of energy and other substances in Mollisol. Based on the above, it is found that TCE significantly affected nitrification and denitrification in Mollisol, thus the nitrogen transformation in Mollisol was affected by TCE contamination.

Nitrogen cycling during wastewater treatment

Many wastewater treatment plants in the world do not remove reactive nitrogen from wastewater prior to release into the environment. Excess reactive nitrogen not only has a negative impact on human health, it also contributes to air and water pollution, and can cause complex ecosystems to collapse. In order to avoid the deleterious effects of excess reactive nitrogen in the environment, tertiary wastewater treatment practices that ensure the removal of reactive nitrogen species need to be implemented. Many wastewater treatment facilities rely on chemicals for tertiary treatment, however, biological nitrogen removal practices are much more environmentally friendly and cost effective. Therefore, interest in biological treatment is increasing. Biological approaches take advantage of specific groups of microorganisms involved in nitrogen cycling to remove reactive nitrogen from reactor systems by converting ammonia to nitrogen gas. Organisms known to be involved in this process include autotrophic ammonia-oxidizing bacteria, heterotrophic ammonia-oxidizing bacteria, ammonia-oxidizing archaea, anaerobic ammonia oxidizing bacteria (anammox), nitrite-oxidizing bacteria, complete ammonia oxidizers, and dissimilatory nitrate reducing microorganisms. For example, in nitrifying-denitrifying reactors, ammonia- and nitrite-oxidizing bacteria convert ammonia to nitrate and then denitrifying microorganisms reduce nitrate to nonreactive dinitrogen gas. Other nitrogen removal systems (anammox reactors) take advantage of anammox bacteria to convert ammonia to nitrogen gas using NO as an oxidant. A number of promising new biological treatment technologies are emerging and it is hoped that as the cost of these practices goes down more wastewater treatment plants will start to include a tertiary treatment step.

Diversity, structure, and size of N(2)O-producing microbial communities in soils--what matters for their functioning?

Nitrous oxide (N(2)O) is mainly generated via nitrification and denitrification processes in soils and subsequently emitted into the atmosphere where it causes well-known radiative effects. How nitrification and denitrification are affected by proximal and distal controls has been studied extensively in the past. The importance of the underlying microbial communities, however, has been acknowledged only recently. Particularly, the application of molecular methods to study nitrifiers and denitrifiers directly in their habitats enabled addressing how environmental factors influence the diversity, community composition, and size of these functional groups in soils and whether this is of relevance for their functioning and N(2)O production. In this review, we summarize the current knowledge on community-function interrelationships. Aerobic nitrification (ammonia oxidation) and anaerobic denitrification are clearly under different controls. While N(2)O is an obligatory intermediate in denitrification, its production during ammonia oxidation depends on whether nitrite, the end product, is further reduced. Moreover, individual strains vary strongly in their responses to environmental cues, and so does N(2)O production. We therefore conclude that size and structure of both functional groups are relevant with regard to production and emission of N(2)O from soils. Diversity affects on function, however, are much more difficult to assess, as it is not resolved as yet how individual nitrification or denitrification genotypes are related to N(2)O production. More research is needed for further insights into the relation of microbial communities to ecosystem functions, for instance, how the actively nitrifying or denitrifying part of the community may be related to N(2)O emission.

Burkholderia insulsa sp. nov., a facultatively chemolithotrophic bacterium isolated from an arsenic-rich shallow marine hydrothermal system

Enrichment cultures inoculated with hydrothermally influenced nearshore sediment from Papua New Guinea led to the isolation of an arsenic-tolerant, acidophilic, facultatively aerobic bacterial strain designated PNG-April(T). Cells of this strain were Gram-stain-negative, rod-shaped, motile and did not form spores. Strain PNG-April(T) grew at temperatures between 4 °C and 40 °C (optimum 30-37 °C), at pH 3.5 to 8.3 (optimum pH 5-6) and in the presence of up to 2.7% NaCl (optimum 0-1.0%). Both arsenate and arsenite were tolerated up to concentrations of at least 0.5 mM. Metabolism in strain PNG-April(T) was strictly respiratory. Heterotrophic growth occurred with O2 or nitrate as electron acceptors, and aerobic lithoautotrophic growth was observed with thiosulfate or nitrite as electron donors. The novel isolate was capable of N2-fixation. The respiratory quinones were Q-8 and Q-7. Phylogenetically, strain PNG-April(T) belongs to the genus Burkholderia and shares the highest 16S rRNA gene sequence similarity with the type strains of Burkholderia fungorum (99.8%), Burkholderia phytofirmans (98.8%), Burkholderia caledonica (98.4%) and Burkholderia sediminicola (98.4%). Differences from these related species in several physiological characteristics (lipid composition, carbohydrate utilization, enzyme profiles) and DNA-DNA hybridization suggested the isolate represents a novel species of the genus Burkholderia, for which we propose the name Burkholderia insulsa sp. nov. The type strain is PNG-April(T) ( = DSM 28142(T) = LMG 28183(T)).

A great leap forward in microbial ecology

Ribosomal RNA (rRNA) sequence-based molecular techniques emerged in the late 1980s, which completely changed our general view of microbial life. Coincidentally, the Japanese Society of Microbial Ecology (JSME) was founded, and its official journal "Microbes and Environments (M&E)" was launched, in 1985. Thus, the past 25 years have been an exciting and fruitful period for M&E readers and microbiologists as demonstrated by the numerous excellent papers published in M&E. In this minireview, recent progress made in microbial ecology and related fields is summarized, with a special emphasis on 8 landmark areas; the cultivation of uncultured microbes, in situ methods for the assessment of microorganisms and their activities, biofilms, plant microbiology, chemolithotrophic bacteria in early volcanic environments, symbionts of animals and their ecology, wastewater treatment microbiology, and the biodegradation of hazardous organic compounds.